1. Field of the Invention
This invention relates to a compact zoom lens system, and more particularly to a compact zoom lens system suitable for lens shutter cameras, particularly underwater cameras.
2. Description of the Related Art
One type of camera reflecting the trend toward outdoor living in recent years is the underwater camera. An underwater camera must have an optical system suitable for underwater photo-taking. For example, if a zoom lens system suitable for underwater photo-taking is to be realized, the condition that the lens unit that comes in contact with water be motionless during zooming should be met.
One construction to meet this condition is a system in which a fixed non-powered barrier that does not move during zooming is located in front of a second zoom lens unit comprising positive and negative lenses. Conventionally, a system comprising a first lens unit having a negative refractive power, a second lens unit having a positive refractive power and a third lens unit having a negative refractive power, in that order from the object side, in which the second and third lens units are moved for zooming while the first lens unit is fixed during zooming, has been proposed as well (Japanese Laid-Open Patents Sho 64-74521, Hei 1-116615, etc.)
However, with the former construction, because the effective aperture of the barrier is large, the camera cannot be made compact in terms of its height and width. On the other hand, with the latter construction, because the length of the lens system along the optical axis is large, the camera cannot be made compact in terms of its depth.